JPH03131244A - Method and device for particularly improving the repeatability and efficiency of pressure wave taking place between two electrodes during capacitor discharge with conductive liquid medium interposed therebetween and impulse wave generating device using said method and device to conduct stone crushing particularly in liquid - Google Patents

Abstract

PURPOSE: To prevent discharge vibration by remarkably decreasing resistance to a current between electrodes, and setting the resistance to a resistance value close to the critical resistance or a little higher than that. CONSTITUTION: Resistance to a current flowing between electrodes 12, 14 is remarkably decreased to reach a resistance value close to the critical resistance or a little higher than that. In order to decrease the electric resistance, it is desirable to provide a conductive liquid medium partially positioned between the electrodes, and it can be simply accomplished by filling an elliptic reflector 10 with a conductive liquid medium. The conductive liquid medium is let have electric resistance at least 1/10, preferably 1/100 of the value of electric resistance, taking normal ionized water normally having low efficiency of about 1500Ωcm as a reference. That is, the electric resistance of the conductive medium is such that specific resistance of about 20Ωcm or less is desirable, and preferably it ranges from several Ωcm to 20Ωcm. Thus, discharge vibration is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention particularly improves the reproducibility and efficiency of the pressure waves generated between two electrodes during discharge of a capacitor by interposing a conductive liquid between the two electrodes. a method and apparatus for;
It also relates to a shock wave generator using the method or device, particularly for submerged rock crushing.

BACKGROUND OF THE INVENTION A high frequency shock wave generator is known from RIEBIER, US Pat. No. 2,559,227. The device comprises a truncated ellipsoidal reflector 80 in which a shock wave is generated by a discharge or arc between two electrodes arranged to converge on each other at a first focus of the ellipsoid.

The purpose of this device is to destroy the target located at the second focus of the ellipsoid outside the truncated reflector 80 (see Figure 3, column 7, line 51 to column 9, line 30). ).

Electrodes 12 and 13 are made in a highly conductive material such as copper or brass and attached to an insulator 26.

This insulator 26 is pivotally supported by the devices 11a, llb, and the spacing between the electrodes can be adjusted (column 4, lines 42-53, column 8, lines 40-47).
(see line).

In this Lieber device or similar devices, a discharge or arc is created by closing a high voltage switch, causing the capacitor 11 to momentarily discharge, creating a discharge or arc between the electrodes (FIG. 2B).

According to Lieber's device, the circuit associated with the electrode includes a capacitor and also has a self-inductance.

It can be seen that in such a circuit, the discharge of the capacitor is of the damped oscillatory type. In other words, the capacitor discharges and then recharges in the opposite direction to a lower voltage than the initial voltage, which was very high, until the charge contained in the capacitor is exhausted.

At the same time, an arc and plasma are generated between the two electrodes.

As a result, the currents in the two electrodes are also of the damped oscillatory type, as can be seen with reference to FIGS. 1a, 1b and 1c. While Figure 1a shows the time variation of voltage,
FIG. 1b shows the variation of the current in a Lieber-type discharge circuit. It can be seen that when the circuit is closed at time t, the voltage at the electrode ends rises instantaneously to the value of the voltage across the capacitor (see Figure 1a), when the three electrodes are immersed in the liquid (usually water). (1b) is slightly conductive, and for safety and arc ignition, a small current flows between the two electrodes (1b) because a high resistance is connected in parallel to the capacitor feeding the electrodes. figure).

After a given time, t2, which is referred to as the latent period or delay time, an arc occurs between the electrodes. At this moment, as clearly shown in Figure 1b, a current of several K
Ai rises. The arc has extremely low resistance (approximately 1/100
or 1/1000Ω) is a well-known fact. Current during discharge of capacitor in RL type circuit (first
It is because of the low value of this resistance that the voltage (Fig. b) and voltage (Fig. 1a) oscillate.

The energy contained and released in the arc evaporates the liquid (usually water) in which the electrodes are immersed, producing vapor bubbles,
Therefore, a shock wave is generated. The faster this energy dissipates, the more efficient the shock wave is.

In this way, as shown in Figure 1b, due to the oscillating characteristics of the current, the supply of energy to the external medium is
As clearly shown in the figure, it is incremental.

This shows that the faster the liquid, especially water, evaporates, the stronger the pressure wave (and the shorter the pressure rise time).

Therefore, in order to evaporate large amounts of liquid, especially water, large amounts of energy must be transferred.

However, most of the currently known devices are
As shown in Figures 1 and 1b, a damped oscillatory discharge is used to release energy progressively over time (Figure 1c).

In prior document EP-0296912, the applicant presents a first solution for releasing a large part of the energy stored instantaneously or in a relatively short time by charging a capacitor in a discharge circuit between two electrodes. proposed a law. For this reason, a high resistance insulating element (
32) is proposed to increase the electrical resistance on the arc path at least between the electrodes. This solution is completely satisfactory if the initial pressure wave generates a shock wave that is approximately spherical.

Problems to be Solved by the Invention However, the above solution cannot be realized mechanically by turning the lamp due to the small size of the electrode and its mechanical strength against shock waves. Moreover, the main purpose of this particular solution is only to improve the discharge efficiency when the discharge occurs, and does not solve the problem of delay time. Therefore, this method does not improve the reproducibility of the discharge and therefore the reproducibility and efficiency of the pressure waves, nor does it reduce the wear of the electrodes.

GERBER, U.S. Pat. No. 3,559,435, describes the use of a conductive liquid to provide a desirable conductive path for the current to form an arc through which the current flows. (See column 5, line 4). The purpose is therefore to create an arc and a plasma between the two electrodes in a normal discharge. The purpose of the recommended electrolytic layer is to pass the desired current between the two electrodes to create a highly conductive plasma (column 1, line 55).

In any case, Gaber's solution does not change the configuration of the oscillating currents that cause electrode wear or the gradual delivery of energy to the external medium.

Contrary to the above solutions, the aim of the present invention is to prevent discharge oscillations from occurring, thus preventing the formation of arcs or plasma and supplying energy to the external medium between the electrodes in a very short time. It is.

The main objective of the present invention, therefore, is to eliminate almost completely the delay time normally required to generate a discharge between the electrodes, thereby reducing the amount of charge stored in the capacitor of the discharge circuit connected to the two electrodes. The object of the invention is to solve the new technical problem of providing a solution that makes it possible to transmit a large part of energy instantly in a relatively short time.

Another object of the invention is to make it possible to almost completely eliminate the delay time when generating a discharge between two electrodes and, in particular, to reduce the generation of the discharge current and therefore the vapor bubbles generated thereby. The object of the present invention is to provide a solution that significantly improves the localization of the pressure waves generated during the discharge, thereby greatly increasing the reproducibility and efficiency of the pressure waves generated during the discharge.

Furthermore, another object of the present invention is to make it possible to almost completely eliminate the delay time when generating a discharge between two electrodes, and to reduce the amount of time that is stored by charging the capacitor of the discharge circuit connected to the electrodes. To solve the new technical problem of providing a solution for releasing a large part of the energy immediately or in a relatively short time to create a critically damped discharge, thereby preventing the oscillations associated with the formation of the arc. That's true.

Furthermore, another object of the invention is to solve the above-mentioned new technical problem and to provide a solution that reduces electrode wear.

Another object of the present invention is the use of pressure waves in particular to
To solve the above-mentioned new technical problems with a device for the ex vivo destruction of kidney stones, gallstones and urinary stones (kidney stones, gallstones and urinary stones) or tissues (tumors, etc.), as well as for the treatment of bone fractures, in an extremely simple manner that can be used on an industrial scale. That's true.

All of the above new technical challenges can be met in a satisfactory manner.
This problem was solved for the first time by the present invention at a low cost and at an industrial level.

Means for Solving the Problems According to a first feature of the present invention, there is provided a method for improving a discharge state occurring in a liquid medium such as water between at least two discharge electrodes, the method comprising: A method is provided which is characterized in that the resistance to the resistance is significantly reduced and the resistance is close to the critical resistance or slightly higher.

According to a particularly preferred embodiment of the invention, the electrical resistance is
Reduced by using a conductive liquid medium interposed at least between the electrodes.

According to a particularly advantageous embodiment of the invention, the electrical resistance of the electrically conductive liquid medium used is at least 1/10, more preferably at least 1/100, of its electrical resistance value, based on normal ionized water. . More preferably,
The electrical resistance of the conductive medium according to the invention is approximately 2
It is preferably 0 Ωcm or less, and preferably between several Ωcm and 20 Ωcm.

The conductive liquid medium may consist of an aqueous or non-aqueous electrolyte. Suitable aqueous electrolytes include ionizable compounds, especially halogenated salts such as NaCl, NHaCl, or salts such as sulphates or nitrates containing alkali metals or alkaline earth metals or transition metals such as copper. It is water that contains

Currently preferred conductive aqueous liquid media are 100 or 20
Contains salt at a rate of 0 g/f and has a resistivity of 10 to 50 cI
Il water. Suitable non-aqueous conductive media are conductive oils made electrically conductive by the addition of conductive particles, such as metal particles, known to those skilled in the art.

According to a second feature of the present invention, there is provided an apparatus for improving the state of a discharge occurring in a liquid medium such as water between at least two discharge electrodes to which current is intermittently supplied, the apparatus comprising: By reducing the resistance to current between the electrodes,
To provide a device having means for achieving a resistance value close to or slightly higher than the critical resistance.

According to a particularly advantageous embodiment, the means for reducing the electrical resistance to electric current comprises an electrically conductive liquid medium interposed between at least the electrodes. This intervention is achieved by immersing the electrode in the electrically conductive liquid medium or by pouring this electrically conductive liquid medium at the level of the electrode.

Other features of the electrically conductive liquid medium according to the invention, which have been described with respect to the method, are of course also applicable to the apparatus.

According to the invention, since the discharge is generated through a conductive medium, the delay time can be almost completely eliminated. Furthermore, the reproducibility of the pressure waves generated between the electrodes is considerably improved and vibrations associated with arc formation are avoided. this is,
This is mainly because the localization of the bubble formation was inaccurate in the conventional case because arcs occurred randomly both in time and space, but this is not the case in the present invention. Therefore, according to the invention, the dynamic current is eliminated and the discharge is of the critically damped type. This will be more easily understood from the following explanation with reference to the drawings in Attachment A4.

Furthermore, according to the present invention, the energy is more instantaneously (
(at a critical speed), the pressure generated is 0 when the discharge voltage of the capacitor is the same value, which is higher than that of the conventional case.

The present invention therefore realizes the various technical advantages described above that were not anticipated or obvious to anyone skilled in the art.

Other features, features and advantages of the invention will become clearer from the description given below, with reference to the accompanying drawings, which show a preferred embodiment of the device, given by way of non-limiting example. Dew.

Figure 2 shows Lieber's United States Patent Box 2゜559.
A truncated elliptical reflector of the type described in , No. 227, is shown schematically for reference and designated by the reference numeral 10. This 1/F 1 noctor comprises two electrodes 12.14, which are located opposite each other so as to converge towards an internal focus indicated by the reference symbol F.

A second focal point of the ellipsoid is located on the exterior of the truncated elliptical reflector 10, and the target to be destroyed is aligned with this second focal point, as described in detail in the Lieber patent. Of course, this target may also be a stone.

The electrode 12 is, for example, grounded as shown in FIG.
Furthermore, it is connected to one end of the capacitor C.

The other electrode 14 is, for example, a resealable bag for a gas arc-extinguishing circuit breaker, etc.]
It is connected to capacitor C via.

This switching device is intermittently shut off by a control device designated by reference numeral 20. A high value resistor R is placed in parallel with the capacitor C. Capacitor C may be described, for example, in document EP-8-02969 by the applicant, which is cited for reference.
10,000 from the power supply as shown in Figure 1 of No. 12.
A high voltage of =20.000 V is charged. The corresponding circuit has been omitted for ease of understanding. Typically, the elliptical reflector 10 is filled with a shock wave transmitting fluid, usually water, and has considerable resistance to electrical current. Normally, the electrical resistance value of ionized water is approximately 1500Ωcm in terms of resistivity.
It is. Lieber's United States Patent Box 2.559.
In the case of highly insulating oils, such as No. 227, the resistivity is approximately 3-5 MΩcm.

When the liquid medium between the electrodes 12.14 is usually ionized water, when a discharge occurs in a circuit as shown in FIG. 2, the discharge as shown in FIGS. 1a, 1b and 1c occurs. Characteristically, there is a considerable delay time, and the state of the discharge is of the oscillatory type, accompanied by the formation of an arc, and which transfers energy to the external medium in stages.

According to the invention, measures are used to significantly reduce the resistance to at least the current flowing between the electrodes 12 to a value close to or slightly above the critical resistance. This solution is based on the applicant's document B, which proposes interposing an insulating element between the electrodes to considerably increase the electrical resistance between them.
This is the opposite of the method recommended in P-A-0296912,
It is also in contrast to the method proposed in Gerber, US Pat. No. 3,559,435.

According to the invention, the means for reducing the electrical resistance preferably comprises an electrically conductive liquid medium located at least partially between the electrodes. In practice, this can be greatly improved by immersing the electrode in a conductive medium, i.e. by filling the elliptical reflector 10 with a conductive liquid medium, i.e. when generating pressure waves in a liquid. can be easily achieved.

According to an advantageous aspect of the invention, the electrically conductive liquid medium has an electrical resistance of at least 1/10 of the value of normal ionized water, which typically has a resistivity of the order of 1500 Ωcm.
, preferably has an electrical resistance of 1/100. The electrical resistance of the conductive medium according to the invention is approximately 200 in terms of resistivity.
Cm or less is desirable, and furthermore, from several Ωcm to 200am
It is preferable that it is in the range of . Thus, the resistance (of the liquid between the electrodes) is the critical resistance (generally 0.3 to several Ωcm).
equal to or very close to. As a result, an electric current flows through the conductive liquid and heats it in the shortest possible time. Considering the values of external parameters such as the capacitance C of the capacitor and the inductance L of the discharge circuit, gas pressure wave generating bubbles are generated almost in the absence of plasma.

Any aqueous or non-aqueous conductive liquid can be used as the conductive medium according to the invention.

Suitable aqueous conductive liquids are aqueous electrolytes made by adding to pure water ionizable soluble compounds such as /% chlorides, especially salts such as chlorides, sulfates, nitrates, etc. . A particularly desirable aqueous electrolyte is NaCl or NH,C
This is water to which I has been added. A more preferable medium has a resistivity of 10 to 5 Ωcm and a concentration of 100 or 200 g/f.
It is salt water. Suitable non-aqueous electrolytes include conductive oils, ie oils made electrically conductive by the addition of conductive particles, such as metal particles.

According to the invention, using a conductive medium, FIG. 3a, FIG.
The discharge characteristics are obtained as shown in Figure b and Figure 3C.

The electrodes are connected for a time of 1. As soon as the capacitor C is ignited, the discharge of the capacitor C occurs almost instantaneously.

Furthermore, the discharge is of the critically damped type and not of the sinusoidal type. Also, since the energy is delivered to the external medium in a much shorter time than in oscillating conditions or in conventional conditions with a delay time, the value of the generated pressure wave can be increased in a shorter time.

As a result, the discharges do not occur randomly in time and space, but, on the contrary, at times 1. The reproducibility of the pressure wave is considerably high due to the formation of completely localized vapor bubbles. The graph shown in FIG.
salt water with a concentration of 200 g/A as a conductive medium for immersing the electrodes, a capacitor with a capacity of 100 nF, and a spacing between the electrodes of 0.
4 mm and an overall self-inductance L of 80 nH using the discharge circuit shown in FIG.

In this specification, an electrode whose critical resistance substantially satisfies the formula: %formula %) (where L is the value of the internal self-inductance of the discharge circuit of the capacitor C, and C is the capacitance value of the capacitor) Note that the resistance value is between.

According to the invention, excellent pressure wave reproducibility with an average deviation of less than 5% is obtained using conductive liquid media, especially when using salt water. On the other hand, when ordinary ionized water is used, the average deviation is about 30%. Therefore, the present invention provides unexpected technical advantages that were not obvious to those skilled in the art, and thus solves all of the aforementioned problems. The invention also provides the possibility of implementing the method described above.

Finally, the present invention is a pressure wave generating device that generates pressure waves by passing a current between two electrodes, characterized in that it uses the method or device for improving the discharge state described above. We will also realize a device that does this. In particular, this pressure wave generator is characterized in that it comprises a truncated elliptical reflector filled with an electrically conductive liquid medium according to the invention.

The above pressure wave generator is used to generate stones (kidney stones, etc.) caused by pressure waves.
It is desirable to apply it to the destruction of gallstones, urinary stones) or tissues (tumors, etc.) from outside the body, and furthermore to the treatment of bone fractures.

4. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a, 1b, and 1c are based on Lieber, U.S. Pat. No. 2,559.2, schematically shown in FIG.
Figure 2 is a graph showing the voltage, current and energy curves, respectively, during a normal arc discharge between two electrodes using a discharge circuit according to No. 27;
, a partial cross-section of a truncated elliptical reflector of the type described in No. 227, taken along a section passing through the electrode and the internal focal point of the truncated elliptical reflector, and a capacitor charging/discharging circuit connected to the electrode. 3a, 3b and 3c schematically show a resistor R arranged in parallel with a capacitor; FIGS. 3a, 3b and 3c show that according to the invention,
1a, 1b and 1c respectively showing the voltage, current and energy curves obtained when using a conductive liquid medium at least between the electrodes; FIG.

(Main reference number) 10...Reflector, 20...control device, C... Capacitor, R...Resistance 12.14...electrode, F. Internal focus, ■...Switching device,

Claims (14)

[Claims] (1) A method for particularly improving the reproducibility of a discharge state that occurs in a liquid medium such as water between at least two electrodes to which a current is intermittently supplied, the method comprising: reducing the resistance to the current at least between the electrodes; A method characterized in that the resistance is significantly reduced to a value close to the critical resistance or slightly higher. 2. The method according to claim 1, characterized in that: (2) a conductive liquid medium is used so as to be interposed at least between the electrodes. (3) The electrical resistance of the conductive liquid medium is at least 1/1 of the electrical resistance value of normal ionized water.
2. A method according to claim 1, characterized in that it is 0, preferably at least 1/100. (4) The electrical resistance of the conductive liquid medium is about - in terms of resistivity.
20Ωcm or less, preferably from several Ωcm to 20Ωcm
4. A method according to claim 3, characterized in that the range is between . 5. A method according to claim 2, characterized in that the electrically conductive liquid medium is an aqueous or non-aqueous electrolyte, preferably salt water. (6) A device for improving a discharge state that occurs in a liquid medium such as water between at least two electrodes to which current is intermittently supplied, the device significantly reducing the resistance to the current at least between the electrodes, and A device characterized by comprising means for increasing the resistance to a value close to or slightly higher than the critical resistance. 7. Device according to claim 6, characterized in that said means comprises at least a conductive liquid medium interposed between the electrodes or injected at the level of the electrodes. (8) The electrical resistance of the electrically conductive liquid medium is at least 1/10, preferably at least 1/100 of the electrical resistance value of normal ionized water in terms of resistivity. 6. The device according to 6. (9) A device according to claim 8, characterized in that said conductive liquid medium consists of an aqueous or non-aqueous electrolyte. (10) Claim characterized in that the conductive liquid medium is an aqueous electrolyte prepared from pure water to which an ionizable compound is added, in particular a salt such as a halide salt, sulfate or nitrate. 7. The device according to 7. (11) The conductive liquid medium has a resistivity of about 20 Ωcm, such as salt water with a concentration of 100 or 200 g/l.
8. Device according to claim 7, characterized in that it has an electrical resistance of: (12) A device for generating pressure waves by passing a current between two electrodes, comprising the device according to any one of claims 6 to 11, or any one of claims 1 to 5. A pressure wave generator characterized in that the method according to item 1 is used. (13) A pressure wave generating device, characterized in that it comprises a truncated elliptical reflector (10), which reflector is filled with the electrically conductive liquid according to any one of claims 6 to 11. (14) The device according to claim 12, wherein the device is used to destroy stones (kidney stones, gallstones, and urinary stones) or tissues (tumors, etc.) from outside the body using pressure waves, and to treat bone fractures. equipment.